29 April 2010

A few years ago, a bonnethead shark made the news because one had given birth. Giving birth is not unusual for sharks... except that the female in question had grown up in isolation. Good evidence for parthenogenesis.

Shortly after that, another shark species (blacktip) was autopsied and found to have an embryo that was genetically identical to the mother. Clearly, parthenogenesis in sharks was not happenstance. But in both cases, the parthenogenetic offspring didn’t live long. Are the offspring able to make it to adulthood?

A new paper examined this in white spotted bamboo shark (Chiloscyllium plagiosum). It came to an aquarium as a juvenile, and kept laying eggs that were discarded as nonviable... until word got out about the bonnethead shark, and one of the savvy keepers decided to start keeping the cases. Out of seven eggs, four hatched. One died young, one “committed suicide” (jumped out of the tank), and the other two grew up to be find, upstanding bamboo shark ladies.

DNA testing confirmed that the offspring had the same genetic make-up as the mother. Definitely parthenogenesis going on here.

Feldheim and colleagues also note that the bamboo sharks they tested in aquaria seemed to be quite inbred. They seem to be hinting that this inbreeding may be facilitating parthenogenetic reproduction. With so few individuals to work with at this point, it’s too early to tell.

What is particularly cool and exciting about this finding is not just the evidence that these shark clones are perfectly viable and can live to adulthood, but this particular species is in a completely different order of sharks compared to the previous two species. That means the capability is either very widespread, or has evolved multiple times. Either way, the ecological and evolutionary importance of parthenogenesis in this group is larger than expected.

13 April 2010

This is a word that a new paper in Proceedings of the Royal Society of London B had added to my vocabulary. It refers to how an unfertilized egg in a normally sexual species can sometimes develop into a female and hatch. If that turns out to be possible, you have a small foothold that natural selection can work on, providing a way that a species can gradually become asexual.

Hybridization seems to be the most common pathway to parthenogenesis, though.

Picture of Tycho crater by Michael Karrer on Flickr, and used under a Creative Commons license.

01 April 2010

Science magazine is reporting (paywall) that the government of Madagascar is reversing a decision to log rosewood. Madagascar’s natural ecosystems are still very much under pressure, though, and they are a dangerous places:

(S)tudying Madagascar's forests has become dangerous. Fisher says visitors are sometimes threatened by organized criminal loggers. During his recent survey of the northeastern forests, he says, “we had to monitor our food for possible poisoning.” He found only a single unpaid ranger “confronting the lemur trappers and loggers. ... His life is continually threatened.”

Tracking the spread of Marmorkrebs in Madagascar is probably going to be nigh impossible for a while.